diff --git a/src/main/scala/lisa/proven/mathematics/SetTheory.scala b/src/main/scala/lisa/proven/mathematics/SetTheory.scala
index d677546eeb23f6de0b4453a9e8fdfb471142cdf2..611c82a5ff955d87ce2b3d51a91ec96861be7c61 100644
--- a/src/main/scala/lisa/proven/mathematics/SetTheory.scala
+++ b/src/main/scala/lisa/proven/mathematics/SetTheory.scala
@@ -359,7 +359,7 @@ object SetTheory extends lisa.Main {
 
   private val x = VariableLabel("x")
   private val y = VariableLabel("y")
-  val oPair: ConstantFunctionLabel = DEFINE("", x, y) as pair(pair(x, y), pair(x, x))
+  val oPair: ConstantFunctionLabel = DEFINE("pair", x, y) as unorderedPair(unorderedPair(x, y), unorderedPair(x, x))
   show
 
 }